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3-4 Receiving & Installation MN2411
Use of Electric Motor Loads
Electric motors require much more current (amperes) to start them than to keep them running.
Some motors, particularly split−phase motors are very difficult to start and require 5 to 7 times
more current to start them. Repulsion−induction type motors are the easiest to start and normally
only require 2 to 3 times as much current to start them.
Most fractional horsepower motors take about the same amount of current to start them and
keep them running. This is true whether they are the repulsion−induction type motor, capacitor
type motor, or the split−phase type motor.
Other factors that influence the amount of current needed to start a motor are:
1. The type of load connected to the motor. If the electric motor is connected to a hard
starting load such as an air compressor it will require more starting current. If the same
electric motor is connected to a light load such as a heater or power saw it will require
less starting current.
2. The brand or design of the electric motor. The expected starting current for a
particular size motor will vary depending on the brand of the electric motor as well as
the type of electric motor (Split Phase, capacitor, Repulsion−induction type, etc.)
3. The condition of the electric motor. A clean motor with free turning bearings will
require less starting currents than a similar type motor that is dirty and the bearings are
not as free turning as they used to be.